Patients with drug resistant epilepsy undergo multimodal evaluation by neurologists and neurosurgeons before deciding on an appropriate treatment regimen. The multimodal evaluation may include electroencephalograph (EEG) measurements taken using a scalp electrode array, magnetic resonance imaging (MRI), and positive emission tomography (PET) imaging to identify a target region of the patient's brain for resection. The goal of these evaluations is to accurately identify the portion of the brain generating seizures so that it may be surgically resected with the goal of eliminating seizures and curing the patient of epilepsy.
Some patients undergo more invasive (Phase II) monitoring with intracranial electrodes. For such patients, intracranial electrodes are implanted in the patient. The goal is to center the intracranial electrodes over the region of the patient's brain that is causing seizures in order to capture as much information about the seizures as possible. After implantation, the patient is typically monitored for a period of two weeks to identify a resection target. The implanted electrodes are then removed and the resection target (epileptogenic focus) is removed during neurosurgery.
One problem that occurs during intracranial electrode implantation is the potential for inaccurate positioning of the electrode array with respect to the region of the brain causing seizures. In instances when noninvasive modalities are unable to provide precise information regarding the location of seizure onset, the electrode array may be placed such that only an edge of the electrode array is located over the region of the brain causing seizures. When this occurs, additional surgery may be required to reposition the electrode and repeat the Phase II monitoring.
Even when the electrode array was placed properly during Phase II monitoring, the electrode array must be removed at the time of surgical resection of the epileptogenic focus. Accordingly, the surgeon is required to remember which regions of the electrode array correspond to the regions of the brain causing the seizures without a direct reference after removal of the electrode array.
It is desirable to identify and visualize neurophysiologic biomarkers, such as those that predict or indicate seizure activity, during electrode implantation, during Phase II monitoring, and during resection surgery. However, due to growing volumes of data and the amount of processing that is required to visualize the data, systems that provide such real time visualization are not currently available. For example, raw EEG data is usually presented in two dimensional plots of detected voltage versus time. In order to be clinically useful during surgery, the occurrence of neurophysiologic biomarkers, such as high frequency oscillations, must be identified, and the occurrences must be mapped to locations of the electrodes in two dimensions or to the occurrences in an image of the patient's brain in three dimensions. With the number of electrodes in implanted electrode arrays increasing, the amount of data that must be processed has heretofore made the real time production of such an image impractical.
One particular problem that occurs during epilepsy surgery is mapping of the resection target identified preoperatively to the surgical field. Resection surgery for epilepsy is difficult because brain tissue affected by epilepsy appears visually normal. In current common practice, the preoperatively identified resection target is manually drawn on a two-dimensional cartoon of the brain for the surgeon to review interoperatively and subsequently transpose onto the surgical field. Such transposition leads to potential errors in identifying the proper resection target.
Accordingly, in light of these difficulties, there exists a need for methods, systems, and computer readable media for visualization of a resection target during epilepsy surgery and for real time spatiotemporal visualization of neurophysiologic biomarkers.